Leads implanted in or about the heart have been used to reverse certain life threatening arrhythmias, or to stimulate contraction of the heart. Electrical energy is applied to the heart via the leads to return the heart to normal rhythm. Leads have also been used to sense in the atrium or ventricle of the heart and to deliver pacing pulses to the atrium or ventricle.
The lead includes one or more conductors to conduct energy from the pacemaker to the heart, and also to receive signals from the heart. In a typical construction, one conductor goes to the band electrode proximally (outer electrode) and another conductor goes to the tip electrode at the distal end (inner electrode). The conductors run side by side and are insulated from each other and also from the body. The insulation is typically a polymer tubing or covering over the lead body. These polymeric materials must demonstrate resistance to hydrolysis and degradation by oxides found in the body. These polymeric materials must also demonstrate appropriate mechanical and electrical properties for use as electrical stimulation leads.
Silicone rubber and polyurethanes have been used most commonly to insulate leads. The silicone rubbers have excellent biocompatibility and long-term stability but they have weak tensile strength and low abrasion resistance. Polyurethanes are less thrombogenic than silicone rubber and higher in tensile strength. In addition, they slide easily against one another when moistened with body fluids. However, polyurethanes tend to be stiffer and not as pliable as silicone rubber.
Currently, leads are sometimes manufactured with a proximal polyurethane section and a distal silicone section. To achieve the required insulative properties, separate silicone and polyurethane composite tubing are layered over the lead.
Accordingly, there is a need for a lead insulation that has flexible material resistance and has improved lubricity.